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No TX power [SOLVED]

For the benefit of all users, this how I fixed my X6100 which showed 100ALC no TX power. I was using the radio as normal on CW and the TX power became intermittent. Then gone in a few more seconds.

In this thread I have documented many tests, voltages and items that @Real and I discovered and other people helped us look at.?

Shortly after the failure, I noticed that switching the RX ATT on actually allowed the TX to work again (this was tried and worked several times .. odd!)?

After a few attempts the TX power failed and never came back.

I tried flashing and refreshing many firmware - nothing worked.?

Yesterday I removed the AFT final output FET transistor and it was obvious now that something was wrong. On my radio version there was some type of rubberised compound or gasket around the FET and heatsink. The heatsink PUSHES though the PCB onto the BACK of the FET. The Source of the FET is held against this heatsink which is also a connection to the PCB. The Drain and Gate are soldered directly (the two tabs on the FET).?

The gasket had clearly melted or the adhesive failed and lots of clear sticky substance had flooded under the FET between the heatsink.

The Source of the FET (back plate) was lumpy and sort of corroded really... I used alcohol and a small file to clean and dress both the FET and the heatsink to make a clean mating surface.?

Re soldered the FET back into the radio and it worked first time perfectly. The radio is remaining at a normal temperature and I have full TX power restored.?

I am now using FW 1.1.7 and that is working perfectly along with WFSERVER all working great.?

SO for my radio, the output was not broken. I tested the FET on a breadboard using a DDM meter by charging the gate with the diode mode and observing the drain src conduct. Touching the gate with my finger discharges the gate and current stops flowing.

Hope this helps

Scot
M0RWV?

[UPDATE]
The repair is still good after several days however I have read a lot of literature regarding NXP LDMOS RF devices and the techniques used to heatsink these RF FETS.

I appears that the mounting of the output FET is very technical and completed in highly controlled reflow conditions using special jigs and equipment that the home repair does not have access to (even advanced hobbyist)?

I think the issue with my radio was that the soldered (paste or pre-form) had heated up and pumped out. The whole back of the transistor was a mess. It is not practical to reflow the solder as the temperatures required are difficult to administer.
I have obtained an IC Graphite cooling pad from Innovation Cooling, a graphite pad also recommended by NXP in their literature)?